The goal of this project is to develop a fluid cell sorter capable of operating in a laminar mode at flow rates up to one meter per second and providing switching of a specimen stream while maintaining sheath in all output channels. Following preliminary, theoretical, and conceptual studies, several large-scale models were fabricated to evaluate promising geometrical configurations. Extensive testing, further theoretical studies, modifications to design, and retesting have resulted in a preliminary design showing great promise. Upper limits of flow velocity and Reynolds number required for reliable operation were determined. In addition, a maximum cell sorting rate and corresponding minimal cell separation distance were established. This large-scale model is of plexiglass construction permitting visualization of flow and incorporates flow meters on all input and output flow lines. Reynolds numbers are matched at a large-scale model flow velocity of 2.5 cm/second. This corresponds to a final true scale device velocity of one meter per second. The characteristic times for the model are 1,600 times that of the true scale device. This permits easy visualization and photography of the model's dynamic switching behavior. A true scale device has been fabricated based on the design evaluated using the large-scale model. This true scale device is currently undergoing testing. (3)